Process for the preparation of dispersions using viscosity-increase inhibitors of water-soluble polymers

ABSTRACT

A process for producing a water-soluble polymer dispersion comprising polymerizing water-soluble monomers having double bonds in an aqueous salt solution that dissolves the monomers but does not dissolve the formed polymer while stirring in the presence of a dispersant composed of a polymer electrolyte soluble in this aqueous salt solution to obtain fine polymer particles dispersed in the aqueous salt solution, characterized by adding at least one viscosity-increase suppressor selected from the group consisting of: (A) a polyvalent carboxylic acid or a salt thereof, (B) a polyvalent phenol, (C) a cyclic compound containing a hydroxyl group and a carboxyl group or a salt thereof, (D) gluconic acid or a salt thereof, (E) a reaction product obtained by reacting methoxyhydroquinone and/or (meth)acrylic cationic monomer with a compound that generates radicals in an oxidizing atmosphere, (F) a reaction product obtained by reacting (meth)acrylic cationic polymer with a compound that generates radicals in an oxidizing atmosphere, (G) a reaction product obtained by reacting (meth)acrylic cationic polymer with an oxidant, and a mixture thereof.

TECHNICAL FIELD

The present invention relates to a process for producing a dispersion ofa water-soluble polymer having low viscosity and high fluidity,dispersed in an aqueous salt solution as dispersionmedium, and widelyused in, for example, a flocculant and a dewatering agent used as awater treatment agent, paper production chemicals used in a papermakingprocess, a dispersion stabilizer of various types of suspensions or asoil improver, and more particularly, to a process for producing awater-soluble polymer dispersion characterized by adding a specificchemical substance to maintain the viscosity of the reaction solution ata low level during polymerization.

BACKGROUND ART

As an example of a process for producing a dispersion of finewater-soluble polymer particles in an aqueous salt solution asdispersion medium having low viscosity and high fluidity in the priorart, processes comprising polymerizing while stirring in the presence ofa dispersant such as polymer electrolyte are disclosed in EuropeanPatent Publication No. 0183466 and European Patent Publication No.0364175.

In the case of carrying out the processes disclosed in the patentpublications described above, the phenomenon occurs in which theviscosity of the reaction solution increases significantly duringpolymerization. Consequently, a large load is applied to the agitator,thereby creating the need to use a high-powered motor and stirringblades that are able to withstand high levels of torque. This results inthe problem of high cost of the reaction apparatus. In addition, sincethe viscosity of the reaction solution becomes high, there are portionsthat are not mixed properly, thereby resulting in the additional problemof the formation of coarse particles.

DISCLOSURE OF THE INVENTION

As a result of conducting various studies on a process that solves theabove-mentioned problems, the inventors of the present invention foundthat by adding a specific chemical substance to the reaction solution,the increase in viscosity of the reaction solution during polymerizationcan be suppressed, thereby leading to completion of the presentinvention.

Namely, in a process for producing a water-soluble polymer dispersioncomprising polymerizing water-soluble monomers having double bonds in anaqueous salt solution that dissolves the monomers but does not dissolvethe formed polymer while stirring in the presence of a dispersantcomposed of a polymer electrolyte soluble in this aqueous salt solutionto obtain fine polymer particles dispersed in the aqueous salt solution,the present invention suppresses the phenomenon of the significantincrease in viscosity of the reaction solution during polymerization byadding at least one viscosity-increase suppressor selected from thegroup consisting of:

(A) a polyvalent carboxylic acid or a salt thereof,

(B) a polyvalent phenol,

(C) a cyclic compound containing a hydroxyl group and a carboxyl groupor a salt thereof,

(D) gluconic acid or a salt thereof,

(E) a reaction product obtained by reacting methoxyhydroquinone and/or(meth)acrylic cationic monomer with a compound that generates radicalsin an oxidizing atmosphere,

(F) a reaction product obtained by reacting (meth)acrylic cationicpolymer with a compound that generates radicals in an oxidizingatmosphere,

(G) a reaction product obtained by reacting (meth)acrylic cationicpolymer with an oxidant, and a mixture thereof, thereby making itpossible to carry out production even with a low-powered agitator, whilealso reducing the formation of coarse particles.

In the present invention, it is preferable that the water-solublemonomers having double bonds be composed of 0-30 mol % acrylic acid,0-100 mol % acrylamide and 0-100 mol % cationic monomer represented bythe following formula 1 and/or the following formula 2:

(wherein, A represents O or NH, B represents C₂H₄, C₃H₆ or C₃H₅OH, R¹represents H or CH₃, R² and R³ represent an alkyl group having 1-4carbon atoms, R⁴ represents hydrogen, an alkyl group having 1-4 carbonatoms or benzyl group, and X⁻ represents a counter ion);

(wherein, A represents O or NH, B represents C₂H₄, C₃H₆ or C₃H₅OH, R⁵,R⁶, R⁷ and R⁸ represent H or CH₃, and X⁻ represents a counter ion)

In the present invention, it is preferable that said dispersant be acationic polymer electrolyte in which 50-100 mol % of at least one typeof cationic monomer selected from the group consisting ofdimethylaminoethyl(meth)acrylate salt,dimethylaminopropyl(meth)acrylamide salt, di(meth)allylamine salt,(meth)acryloyloxyethyltrimethylammonium chloride,(meth)acrylamidopropyltrimethylammonium chloride,dimethyldiallylammonium chloride and a mixture thereof, and 50-0 mol %acrylamide are polymerized.

In the present invention, it is preferable that a salt that forms theaqueous salt solution be a bivalent anionic salt.

At this time, it is preferable that the (A) polyvalent carboxylic acidor the salt thereof be oxalic acid, adipic acid, tartaric acid, malicacid, phthalic acid and salts thereof.

Further, it is preferable that the (B) polyvalent phenol be resorcinolor pyrogallol.

In addition, it is preferable that the (C) cyclic compound having ahydroxyl group and a carboxyl group be m-hydroxybenzoic acid,p-hydroxybenzoic acid, salicylic acid, gallic acid, tannic acid and asalt thereof.

In addition, the viscosity-increase suppressor (E) can be obtained byreacting a compound that generates radicals in an oxidizing atmospherein a solution containing methoxyhydroquinone and/or (meth)acryliccationic monomer.

Furthermore, the viscosity-increase suppressor (F) can be obtained byreacting a compound that generates radicals in an oxidizing atmospherewith (meth)acrylic cationic polymer.

The viscosity-increase suppressor (G) can be obtained by reacting anoxidant with (meth)acrylic cationic polymer.

It is preferable that the total added amount of the viscosity-increasesuppressors listed in (A) through (G) above be from 10 ppm to 10,000 ppmbased on the weight of the reaction mixture.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be explained in detail below.

The present invention is a process for producing a water-soluble polymerdispersion comprising polymerizing water-soluble monomers having doublebonds in an aqueous salt solution that dissolves the monomers but doesnot dissolve the formed polymer while stirring in the presence of adispersant composed of a polymer electrolyte soluble in this aqueoussalt solution to obtain fine polymer particles dispersed in the aqueoussalt solution, characterized by adding at least one viscosity-increasesuppressor selected from the group consisting of:

(A) a polyvalent carboxylic acid or a salt thereof,

(B) a polyvalent phenol,

(C) a cyclic compound containing a hydroxyl group and a carboxyl groupor a salt thereof,

(D) gluconic acid or a salt thereof,

(E) a reaction product obtained by reacting methoxyhydroquinone and/or(meth)acrylic cationic monomer with a compound that generates radicalsin an oxidizing atmosphere,

(F) a reaction product obtained by reacting (meth)acrylic catinicpolymer with a compound that generates radicals in an oxidizingatmosphere,

(G) a reaction product obtained by reacting (meth)acrylic cationicpolymer with an oxidant, and a mixture thereof.

The water-soluble monomer having double bonds used in the presentinvention is suitably selected from cationic monomers such as an aminesalt of dialkylaminoalkyl (meth) acrylate and quaternary compoundsthereof, an amine salt of dialkylaminoalkyl(meth)acrylamide andquaternary compounds thereof, an amine salt of dialkylaminopropyl (meth)acrylamide and quaternary compounds thereof, an amine salt ofdialkylaminohydroxypropyl(meth)acrylamide and quaternary compoundsthereof and diallylamines salt and quaternary compounds thereof;nonionic monomers such as (meth)acrylamide, N-vinylcarboxylic acidamide, acrylonitrile and vinyl acetate; anionic monomers such as(meth)acrylic acid, acrylamide-2-methylpropane sulfonic acid anditaconic acid and their salts; and, mixtures thereof.

Specific examples of these water-soluble monomers having double bondsinclude, but are not limited to, cationic monomers such as ahydrochloride or sulfate of dimethylaminoethyl(meth)acrylate,(meth)acryloyloxyethyltrimethylammonium chloride,(meth)acryloyloxyethyldimethylbenzylammonium chloride, a hydrochlorideor sulfate of dimethylaminopropyl (meth) acrylamide(meth)acrylamidopropyltrimethylammonium chloride,(meth)acrylamidopropyldimethylbenzylammonium chloride, a hydrochlorideor sulfate of dimethylaminohydroxypropyl(meth)acrylate,(meth)acryloyloxyhydroxypropyltrimethylammonium chloride,(meth)acryloyloxyhydroxypropyldimethylbenzylammonium chloride anddiallyldimethylammonium chloride; nonionic monomers such as(meth)acrylamide, N-vinylformamide, N-vinylacetoamide andhydroxyethyl(meth)acrylate; and, anionic monomers such as (meth)acrylicacid, acrylamido-2-methylpropane sulfonic acid and itaconic acid and thelike. In addition, hydrophobic monomers such as acrylonitrile, vinylacetate and styrene or the like can be copolymerized provided that thepolymer remains water-soluble.

Polymers that form the water-soluble polymer dispersion of the presentinvention are polymers of the above-mentioned monomers, and examples ofparticularly useful polymers include homopolymers of cationic monomers,cationic polymers such as copolymers of cationic monomers and nonionicmonomers such as acrylamide, amphoteric polymers such as copolymers ofcationic monomers, nonionic monomers such as acrylamide and anionicmonomers such as acrylic acid, and nonionic polymers such ashomopolymers of nonionic monomers such as acrylamide.

Accordingly, more preferable water-soluble monomers having double bondsthat can be used in the present invention are composed of 0-50 mol %acrylic acid, 0-100 mol % acrylamide and 0-100 mol % cationic monomerrepresented by the following formula 1 and/or the cationic monomerrepresented by the following formula 1 and/or the following formula 2:

(wherein, A represents O or NH, B represents C₂H₄, C₃H₆ or C₃H₅OH, R¹represents H or CH₃, R² and R³ represent an alkyl group having 1-4carbon atoms, R⁴ represents hydrogen, an alkyl group having 1-4 carbonatoms or benzyl group, and X⁻ represents a counter ion);

(wherein, A represents O or NH, B represents C₂H₄, C₃H₆ or C₃H₅OH, R⁵,R⁶, R⁷ and R⁸ represent H or CH₃, and X⁻ represents a counter ion)

The dispersant composed of polymer electrolyte used in the presentinvention is preferably a cationic polymer electrolyte obtained bypolymerizing 50-100 mol % of at least one cationic monomer selected fromthe group consisting of a hydrochloride or sulfate ofdimethylaminoethyl(meth)acrylate, hydrochloride or sulfate ofdimethylaminopropyl(meth)acrylamide,(meth)acrylamidopropyltrimethylammonium chloride, a hydrochloride orsulfate of diallylamine, a hydrochloride or sulfate of dimethallylamine,dimethyldiallylammonium chloride and a mixture thereof, with 50-0 mol %acrylamide. In addition, a polyamine such as polyalkylenepolyamine canalso be used.

In addition, in the case of trying to obtain a dispersion of an anionicpolymer, a polymer or copolymer of an anionic monomer selected from thegroup consisting of a salt of (meth) acrylic acid, a salt ofacrylamido-2-methylpropanesulfonic acid and so forth and a mixturethereof can also be used for the dispersant.

The polymer electrolyte that serves as a dispersant in the presentinvention can be obtained by dissolving a monomer in an aqueous medium,adding a polymerization initiator such as a water-soluble azo-typepolymerization initiator like 2,2′-azobis(2-amidinopropane)2-hydrochloride (abbreviated as V-50) or2,2′-azobis[2-(2-imidazoline-2-yl)propane] 2-hydrochloride (abbreviatedas VA-044), or a water-soluble redox-type polymerization initiator likethe combined use of ammonium persulfate and sodium hydrogensulfite andperforming radical polymerization to obtained the desired dispersant.The reaction temperature of polymerization can be arbitrarily selectedwithin the range of 0-100° C. according to the properties of thepolymerization initiator. The addition of a chain transfer agent such asisopropyl alcohol and mercaptan, which are normally used in radicalpolymerization to adjust molecular weight, can also be arbitrarilyselected. Although polymerization of the polymer electrolyte that servesas a dispersant is normally performed by standing aqueous solutionpolymerization, it is preferable to perform polymerization whilestirring in consideration of product uniformity.

In the present invention, the aqueous salt solution that serves as thedispersion medium of the water-soluble polymer dispersion is an aqueoussalt solution that dissolves both the raw material water-soluble monomerand dispersant composed of polymer electrolyte, but does not dissolvethe fine particles of product polymer. Consequently, a type of salthaving those properties is used in the present invention in the form ofan aqueous salt solution of a concentration at which those propertiesare demonstrated.

Salts suitable for use in the present invention are bivalent anionicsalts like sulfates, while the counter cation is selected from ammoniumion, sodium ion, magnesium ion, aluminum ion and so forth. Specificexamples of salts include ammonium sulfate, ammonium hydrogen sulfate,sodium sulfate, sodium hydrogen sulfate, magnesium sulfate, magnesiumhydrogen sulfate, aluminum sulfate and aluminum hydrogen sulfate.Ammonium sulfate and sodium sulfate in particular are the mostpreferable as salts used in the present invention. In order for thesebivalent anionic salts to have the above-mentioned properties, theconcentration of the salt is selected within the range of 15% by weightto saturation concentration. In addition, monovalent anionic salts suchas sodium chloride and ammonium chloride can also be used in combinationwith the above-mentioned bivalent anionic salts.

Methods for improving the fluidity and so forth of the dispersion byadding various types of salts to the water-soluble polymer dispersionobtained after polymerization are described in the patent publicationsmentioned in the background art, and the arts are incorporated in thepresent invention.

In the obtaining of the above-mentioned polymer fine particles, byadding at least one viscosity-increase suppressor selected from thegroup consisting of (A) a polyvalent carboxylic acid or a salt thereof,(B) a polyvalent phenol, (C) a cyclic compound containing a hydroxylgroup and a carboxyl group or a salt thereof, (D) gluconic acid or asalt thereof, (E) a reaction product obtained by reactingmethoxyhydroquinone (MEHQ) and/or (meth)acrylic cationic monomer with acompound that generates radicals in an oxidizing atmosphere, (F) areaction product obtained by reacting (meth)acrylic cationic polymerwith a compound that generates radicals in an oxidizing atmosphere, (G)a reaction product obtained by reacting (meth) acrylic cationic polymerwith an oxidant, and a mixture thereof, large increases in viscosity ofthe reaction solution during polymerization can be suppressed, therebymaking it possible to carry out production even with a low-poweredagitator while also reducing the formation of coarse particles.

It is preferable that the viscosity-increase suppressor be awater-soluble compound, and even more preferable that is dissolved inthe aqueous salt solution serving as the dispersion medium. Specificexamples of water-soluble compounds among the viscosity-increasesuppressors (A) through (G) include, but are not limited to, thecompounds indicated below.

Specific examples of the (A) polyvalent carboxylic acid or the saltinclude oxalic acid, adipic acid, tartaric acid, malic acid, phthalicacid and their salts.

Specific examples of (B) polyvalent phenols include resorcinol andpyrogallol.

Specific examples of (C) cyclic compounds having a hydroxyl group and acarboxyl group include m-hydroxybenzoic acid, p-hydroxybenzoic acid,salicylic acid, gallic acid, tannic acid and their salts.

Specific examples of (D) viscosity-increase suppressors composed of onetype of water-soluble organic compound selected from gluconic acid andits salts include gluconic acid, sodium gluconate, potassium gluconate,ammonium gluconate and various amine salts of gluconic acid.

In the obtaining of the viscosity-increase suppressor defined in (E), acompound that generates radicals is allowed to react while blowing anoxygen-containing gas into a solution containing MEHQ and/or(meth)acrylic cationic monomer. This compound that generates radicalsmay be the same compound as a polymerization initiator normally used inradical polymerization, examples of which include a water-solubleazo-type polymerization initiator like V-50 or VA-044, or awater-soluble redox-type polymerization initiator like the combined useof ammonium persulfate and sodium hydrogensulfite.

In the obtaining of the viscosity-increase suppressor defined in (F), apolymerization initiator which is a compound that generates radicals,examples of which include a water-soluble azo-type polymerizationinitiator like V-50 or VA-044, or a water-soluble redox-typepolymerization initiator like the combined use of ammonium persulfateand sodium hydrogensulfite, is allowed to react in an oxidizingatmosphere, for example while blowing in oxygen-containing gas, with thedispersant of the present invention composed of polymer electrolyteobtained by polymerization of (meth) acrylic cationic monomer inaccordance with known methods, ultimately enabling the obtaining of aviscosity-increase suppressor similar to (E).

In the obtaining of the viscosity-increase suppressor defined in (G), alow molecular weight oxidized polymer is obtained by oxidizing thedispersant of the present invention composed of polymer electrolyteobtained by polymerization of (meth)acrylic cationic monomer inaccordance with known methods using hydrogen peroxide or halogenoxidant, ultimately allowing the obtaining of a viscosity-increasesuppressor similar to (E) and (F).

Specific examples of (meth) acrylic cationic monomers used to obtain theviscosity-increase suppressors (E), (F) and (G) include cationicmonomers such as a hydrochloride or sulfate ofdimethylaminoethyl(meth)acrylate,(meth)acryloyloxyethyltrimethylammonium chloride,(meth)acryloyloxyethyldimethylbenzylammonium chloride, a hydrochlorideor sulfate of dimethylaminopropyl(meth)acrylamide,(meth)acrylamidopropyltrimethylammonium chloride,(meth)acrylamidopropyldimethylbenzylammonium chloride, a hydrochlorideor sulfate of dimethylaminohydroxypropyl(meth)acrylate,(meth)acryloyloxyhydroxypropyltrimethylammonium chloride,(meth)acryloyloxyhydroxypropyldimethylbenzylammonium chloride, and thelike.

These viscosity-increase suppressors (A) through (G) are added in anamount of 10 ppm to 10,000 ppm relative to the weight of the reactionsolution. If the added amount is 10 ppm or less, effects are notdemonstrated, while if the amount is 10,000 ppm or more, it iseconomically wasteful.

The water-soluble organic compounds specifically listed in theabove-mentioned (A) through (G) were found from experimentalconsiderations, and may be respectively used alone or as a combinationof a plurality of types.

The effect of suppressing viscosity-increase of the reaction system bythese compounds has not been theoretically elucidated. Based onexperimental results, the polymer formed in the reaction solution has ahigher solubility for the aqueous salt solution in which non-polymerizedmonomer is dissolved than the simple aqueous salt solution in which onlythe salt used is dissolved, and viscosity-increase is considered tooccur due to the polymer dissolving in solution prior to precipitation.Thus, since the viscosity-increase suppressors (A) through (G) of thepresent invention promote precipitation of fine particles of polymer,viscosity-increase is suppressed as a result of causing the polymer toprecipitate as fine particles before dissolving in solution, therebyresulting in a decrease in torque applied to the rotary shaft of thereaction apparatus and reducing the occurrence of coarse particlesgenerated accompanying defective stirring.

In order to obtain a dispersion of water-soluble polymer in the presentinvention, monomers, dispersant and viscosity-increase suppressor aredissolved in an aqueous salt solution, a polymerization initiator, suchas a water-soluble azo-type polymerization initiator like V-50 orVA-044, or a water-soluble redox-type polymerization initiator like thecombined use of ammonium persulfate and sodium hydrogensulfite, is addedin a state of oxygen gas removal in a nitrogen atmosphere, and radicalpolymerization is carried out while stirring. The polymerizationreaction temperature can be arbitrarily selected according to theproperties of the polymerization initiator within a range of 0-100° C.The addition of a chain transfer agent like isopropyl alcohol andmercaptan, which are normally used in radical polymerization to adjustmolecular weight, can also be arbitrarily selected. It is necessary toperform stirring at a peripheral speed of at least 1 m/min in order toensure smooth precipitation of polymer fine particles. There is no upperlimit on stirring rate provided the contents do not overflow from theapparatus, and arbitrary stirring conditions can be selected.

A known arbitrary charge method can be employed for charging monomer,examples of which include a method in which the entire amount of monomeris charged into the reaction vessel in advance, a method in which aportion of monomer is charged into the reaction vessel in advance afterwhich the remainder of monomer is added continuously, and a method inwhich the entire amount of monomer is added continuously duringpolymerization.

EXAMPLES

Although a detailed explanation of the present invention is providedthrough by means of examples, the present invention is not limited tothe following embodiments provided that its scope is not departed.

Examples 1-15

The monomers having compositions and molar ratios listed in Table 1, thewater-soluble organic compounds (A) through (D) as a viscosity-increasesuppressor listed in Table 1 in the amounts listed in Table 1, and 1part of polydimethyldiallylammonium chloride (manufactured by CPS Corp.,trade name: Age Flock WT40HV) and 1 part ofpolymethacryloyloxyethyltrimethylammonium chloride (intrinsic viscosity:2 dl/g) as dispersants were charged in a reaction vessel (innerdiameter: 70 cm, volume: 270 liters) equipped with a stirrer, nitrogenaeration tube, temperature controller and helical ribbon impeller(diameter: 65 cm, rotating speed: 60 rpm) followed by the addition ofdeionized water and ammonium sulfate to reach the monomer concentrationsand ammonium sulfate concentrations listed in Table 1 and dissolving bystirring to form a uniform solution. Next, a 5% by weight aqueoussolution of V-50 was added as a polymerization initiator in an amount of100 ppm per monomers followed by stirring and polymerization was carriedout for 10 hours at 48° C. As a result, polymer dispersions wereobtained comprising fine particles having a particle diameter of 10-20μm dispersed in an aqueous salt solution.

The maximum values of torque loaded to the rotary shaft of the agitatorduring the polymerization reaction are shown in Table 1. In addition,the results of weighing the amount of polymer remaining on a sieve(coarse particles) after filtering the resulting polymer dispersionthrough a 40 mesh standard stainless steel sieve are shown in Table 1.

Comparative Examples 1-4

With the exception of not adding water-soluble organic compounds (A)through (D) as viscosity-increase suppressors, the same procedure wasperformed as in Synthetic Examples 1-15. The maximum values of torqueloaded to the rotary shaft of the agitator during the polymerizationreaction, and the results of weighing the amount of coarse particles areshown in Table 1.

TABLE 1 viscosity-increase Monomer Ammonium sulfate supressorconcentration concentration Amt. added (ppm, Amt. on Monomer composition(mol %) (%, vs. reaction (%, vs. reaction vs. reaction Max. torque 40mesh filter DMABC DMQ AAM AAC solution) solution) Type solution) (kgf.m)(wt %) Examples 1  0 10 90 0 15.0 29.0 A5 2000 1.2 0.7 C3  500 2  0 1090 0 15.0 29.0 B1 2500 0.8 1.1 C4  100 D1 2500 3  0 10 90 0 15.0 29.0 A25000 0.8 0.9 D1 1000 4 15 20 65 0 20.0 20.0 B2 5000 1.0 1.0 5 15 20 65 020.0 20.0 B1 3000 1.2 0.8 D1 1000 6 15 20 65 0 20.0 20.0 A1 6000 1.4 0.9C4  100 7 15 20 65 0 20.0 20.0 A3 7000 1.6 1.1 8 30 50 20 0 25.0 19.0 B12000 1.5 0.9 C1  50 9 30 50 20 0 25.0 19.0 A2 5000 1.5 0.9 C4  50 10  3050 20 0 25.0 19.0 B2 2500 1.2 0.8 C2  50 11  30 50 20 0 25.0 19.0 A42000 1.3 0.8 B1 1500 12  15 20 60 5 20.0 20.0 D1 4000 1.6 0.9 13  15 2060 5 20.0 20.0 C4  50 1.0 1.1 D1 3000 14  15 20 60 5 20.0 20.0 C5  5000.9 0.8 15  15 20 60 5 20.0 20.0 B1 1000 1.4 1.0 Comparative 1  0 10 900 15.0 29.0 — — 4.5 54   Examples 2 15 20 65 0 20.0 20.0 — — 4.5 38   330 50 20 0 25.0 19.0 — — 4.0 14   4 15 20 60 5 20.0 20.0 — — 4.5 47  ABBREVIATIONS USED IN TABLE: DMABC:Acryloyloxyethyldimethylbenzylammonium chloride DMQ:Acryloyloxyethyltrimethylammonium chloride AAM: Acrylamide AAC: Acrylicacid A1: Oxalic acid A2: Adipic acid A3: Tartaric acid A4: Malic acidA5: Phthalic acid B1: Resorcinol B2: Pyrogallol C1: m-hydroxybenzoicacid C2: p-hydroxybenzoic acid C3: Salicylic acid C4: Gallic acid C5:Tannic acid D1: Sodium gluconate

(Viscosity-increase suppressor Production Example—E1)

10,000 ppm relative to the amount of monomer of a 1% aqueous solution ofV-50 were added to a 1% aqueous solution ofmethacryloyloxyethyltrimethylammonium chloride followed by allowing tostand for 10 hours after heating to 55° C. while stirring and blowing inair to obtain a brown reaction product. This was designated as anaqueous solution having a 1% concentration of viscosity-increasesuppressor E1.

(Viscosity-increase suppressor Production Example—E2)

3,000 ppm relative to the amount of monomer of hydrogen peroxide and9000 ppm relative to the amount of monomer of ferrous sulfate were addedto a 1% aqueous solution of methacryloyloxyethyltrimethylammoniumchloride followed by allowing to stand for 10 hours to obtain a brownreaction product. This was designated as an aqueous solution having a 1%concentration of viscosity-increase suppressor E2.

(Viscosity-increase suppressor Production Example—E3)

5000 ppm relative to the amount of MEHQ of V-50 were added to an aqueoussolution containing 1000 ppm of MEHQ followed by allowing to stand for10 hours after heating to 55° C. while stirring and blowing in air toobtain a brown reaction product. This was designated as an aqueoussolution having a concentration of 1000 ppm of viscosity-increasesuppressor E3.

(Viscosity-increase suppressor Production Example—F1)

5000 ppm relative to the amount of monomer of VA-044 were added to a 3%aqueous solution of methacryloyloxyethyltrimethylammonium chloridefollowed by allowing to stand for 10 hours at 50° C. in a state ofoxygen gas removal in a nitrogen atmosphere to obtain a polymer solutionhaving an intrinsic viscosity of 0.3 dl/g. 5000 ppm of VA-044 werefurther added to this polymer solution followed by allowing to stand for10 hours after heating to 55° C. while stirring and blowing in air toobtain a brown reaction product. This was designated as an aqueoussolution having a concentration of 3% of viscosity-increase suppressorF1.

(Viscosity-increase suppressor Production Example—G1)

1000 ppm relative to the amount of monomer of VA-044 were added to a 10%aqueous solution of methacryloyloxyethyltrimethylammonium chloridefollowed by polymerization for 10 hours at 50° C. in a oxygen gasremoval state in a nitrogen atmosphere to obtain a polymer solutionhaving an intrinsic viscosity of 1.8 dl/g. 500 ppm relative to theamount of polymer of hydrogen peroxide were further added to thispolymer solution followed by diluting to a polymer concentration of 5%with deionized water and allowing to stand for 10 hours at 40° C. toobtain a brown reaction product. This was designated as an aqueoussolution having a concentration of 5% of viscosity-increase suppressorG1.

Examples 16-31

With the exception of using the viscosity-increase suppressors describedin Table 2, the same procedures as Synthetic Examples 1-15 wereperformed to obtain polymer dispersions containing fine particles havinga particle diameter of 10-20 □m dispersed in an aqueous salt solution.The maximum values of torque applied to the rotary shaft of the agitatorduring the polymerization reaction are shown in Table 2. In addition,the results of weighing the amount of polymer remaining on a sieve(coarse particles) after filtering the resulting polymer dispersionthrough a 40 mesh standard stainless steel sieve are shown in Table 2.

Comparative Examples 5-8

With the exception of not using viscosity-increase suppressors, the sameprocedures were performed as in Synthesis Embodiments 16-31. The maximumvalues of torque applied to the rotary shaft of the agitator during thepolymerization reaction, and the results of weighing the amount ofcoarse particles are shown in Table 2.

TABLE 2 viscosity-increase Monomer Ammonium sulfate supressorconcentration concentration Amt. added (ppm, Amt. on Monomer composition(mol %) (%, vs. reaction (%, vs. reaction vs. reaction Max. torque 40mesh filter DMABC DMQ AAM AAC solution) solution) Type solution) (kgf.m)(wt %) Examples 16 0 10 90 0 15.0 29.0 E1 3000 1.5 1.1 17 15 20 65 020.0 20.0 E2 3000 1.5 0.8 18 30 50 20 0 25.0 19.0 E1 3000 1.4 1.0 19 1520 60 5 20.0 20.0 E2 3000 1.4 0.9 20 0 10 90 0 15.0 29.0 E1 3000 1.3 0.921 15 20 65 0 20.0 20.0 E2 3000 1.3 0.8 22 30 50 20 0 25.0 19.0 E1 30001.3 0.9 23 15 20 60 5 20.0 20.0 E2 3000 1.3 0.8 24 0 10 90 0 15.0 29.0F1 3000 1.5 1.1 25 15 20 65 0 20.0 20.0 G1 3000 1.5 0.8 26 30 50 20 025.0 19.0 E3  150 1.4 1.0 27 15 20 60 5 20.0 20.0 F1 3000 1.4 0.9 28 010 90 0 15.0 29.0 E3  150 1.3 0.9 29 15 20 65 0 20.0 20.0 F1 3000 1.30.8 30 30 50 20 0 25.0 19.0 G1 3000 1.3 0.9 31 15 20 60 5 20.0 20.0 G13000 1.3 0.8 Comparative 5 0 10 90 0 15.0 29.0 — — 4.5 54.0  Exampies 615 20 65 0 20.0 20.0 — — 4.5 38.0  7 30 50 20 0 25.0 19.0 — — 4.5 14.0 8 15 20 60 5 20.0 20.0 — — 4.5 47.0  ABBREVIATIONS USED IN TABLE: DMBAC:Acryloyloxyethyldimethylbenzylammonium chloride DMQ:Acryloyloxyethyltrimethylammonium chloride AAM: Acrylamide AAC: Acrylicacid

Examples 32-35

The monomers having compositions and concentrations listed in Table 3,the compounds (A) through (G) as a viscosity-increase suppressor listedin Table 3 in the amounts listed in Table 3, and 1 part ofpolydimethyldiallylammonium chloride (manufactured by CPS Corp., tradename: Age Flock-WT40HV) and 1 part ofpolyacryloyloxyethyltrimethylammonium chloride (intrinsic viscosity: 2dl/g) as dispersants were charged in the reaction vessel used inExamples 1-31 followed by the addition of deionized water and salt toreach the monomer concentrations and salt concentrations (co-use ofammonium sulfate and sodium sulfate) described in Table 3 and dissolvingby stirring to form a uniform solution. Next, a 5% by weight aqueoussolution of VA-044 was added as polymerization initiator in an amount of100 ppm per monomer followed by stirring and polymerization for 10 hoursat 38° C. As a result, polymer dispersions were obtained comprising fineparticles having a particle diameter of 10-20 μm dispersed in an aqueoussalt solution.

The maximum values of torque loaded to the rotary shaft of the agitatorduring the polymerization reaction are shown in Table 3. In addition,the results of weighing the amount of polymer remaining on a sieve(coarse particles) after filtering the resulting polymer dispersionthrough a 40 mesh standard stainless steel sieve are shown in Table 3.

Comparative Examples 9-10

With the exception of not adding viscosity-increase suppressors, thesame procedures were performed as in Synthesis Examples 32-35. Themaximum values of torque loaded to the rotary shaft of the agitatorduring the polymerization reaction, and the results of weighing thecoarse particles are shown in Table 3.

TABLE 3 Viscosity-increase Monomer suppressor concentration Saltconcentration (%, Amt. added Amt. on 40 (%, vs. vs. reaction solution)(ppm, vs. mesh Monomer composition (mol %) reaction Ammonium Sodiumreaction Max. torque filter DMABC DMQ AAM AAC solution) sulfate sulfateType solution) (kgf.m) (wt %) Examples 32 0 20 80 0 15.0 25.8 3.4 C4  501.4 1.0 D1 2500 33 0 20 80 0 15.0 25.8 3.4 A2 5000 1.4 0.8 D1 200 E11500 34 0 35 65 0 15.0 22.4 6.8 C4  50 1.5 1.0 D1 3500 35 0 35 65 0 15.022.4 6.8 A2 4000 1.5 1.2 D1 1000 G1 3000 Comparative 9 0 20 80 0 15.025.8 3.4 — — 5.6 83.0  Examples 10  0 35 65 0 15.0 22.4 6.8 — — 6.795.0 

INDUSTRIAL APPLICABILITY

The Synthesis Examples of the present invention containing theviscosity-increase suppressors (A) through (G) each reduces maximumtorque values and the amount of coarse particles in comparison with thecomparative synthesis examples of the prior art. Namely, the presentinvention offers advantages in terms of design and operation of thereactor, in terms of quality of the resulting water-soluble polymerdispersion, and offers significant economic effects.

What is claimed is:
 1. A process for producing a water-soluble polymerdispersion comprising polymerizing water-soluble monomers having doublebonds in an aqueous salt solution that dissolves the monomers but doesnot dissolve the formed polymer while stirring in the presence of adispersant composed of a polymer electrolyte soluble in said aqueoussalt solution to obtain fine polymer particles dispersed in the aqueoussalt solution, characterized by adding to the polymerization at leastone viscosity-increase suppressor selected from the group consisting of:(A) a polyvalent carboxylic acid or a salt thereof, (B) a polyvalentphenol, (C) a cyclic compound containing a hydroxyl group and a carboxylgroup or a salt thereof, (D) gluconic acid or a salt thereof, (E) areaction product obtained by reacting methoxyhydroquinone and/or(meth)acrylic cationic monomer with a compound that generates radicalsin an oxidizing atmosphere, (F) a reaction product obtained by reacting(meth)acrylic cationic polymer with a compound that generates radicalsin an oxidizing atmosphere, (G) a reaction product obtained by reacting(meth)acrylic cationic polymer with an oxidant, and a mixture thereof.2. The process for producing a water-soluble polymer dispersion s setforth in claim 1, wherein the water-soluble monomers having double bondsare composed of 0-30 mol % acrylic acid, 0-100 mol % acrylamide and0-100 mol % cationic monomer represented by the following formula 1and/or the following formula 2:

(wherein, A represents O or NH, B represents C₂H₄, C₃H₆ or C₃H₃OH, R¹represents H or CH₃, R² and R³ represent an alkyl group having 1-4carbon atoms, R⁴ represents hydrogen, an alkyl group having 1-4 carbonatoms or benzyl group, and X⁻ represents a counter ion);

(wherein, A represents O or NH, B represents C₂H₄, C₃H₆ or C₃H₅OH, R⁵,R⁶, R⁷ and R⁸ represent H or CH₃, and X⁻ represents a counter ion). 3.The process for producing a water-soluble polymer dispersion as setforth in claim 1, wherein said dispersant is a cationic polymerelectrolyte in which 50-100 mol % of at least one type of cationicmonomer selected from the group consisting ofdimethylaminoethyl(meth)acrylate salt,dimethylaminopropyl(meth)acrylamide salt, di(meth)allylamine salt,(meth)acryloyloxyethyltrimethylammonium chloride,(meth)acrylamidopropyltrimethylammonium chloride,dimethyldiallylammonium chloride and a mixture thereof, and 50-0 mol %acrylamide are polymerized.
 4. The process for producing a water-solublepolymer dispersion as set forth in claim 1, wherein the salt that formsthe aqueous salt solution is a bivalent anionic salt.
 5. The process forproducing a water-soluble polymer dispersion as set forth in claim 1,wherein the (A) polyvalent carboxylic acid or the salt thereof is oneselected from oxalic acid, adipic acid, tartaric acid, malic acid,phthalic acid and salts thereof.
 6. The process for producing awater-soluble polymer dispersion as set forth in claim 1, wherein the(B) polyvalent phenol is resorcinol or pyrogallol.
 7. The process forproducing a water-soluble polymer dispersion as set forth in claim 1,wherein the (C) cyclic compounds having a hydroxyl group and a carboxylgroup is one selected from m-hydroxybenzoic acid, p-hydroxybenzoic acid,salicylic acid, gallic acid, tannic acid and salts thereof.
 8. Theprocess for producing a water-soluble polymer dispersion as set forth inclaim 1, wherein the viscosity-increase suppressor (E) is obtained byreacting a compound that generates radicals in an oxidizing atmospherein a solution containing methoxyhydroquinone and/or (meth)acryliccationic monomer.
 9. The process for producing a water-soluble polymerdispersion as set forth in claim 1, wherein the total added amount ofthe viscosity-increase suppressors represented by (A) through (G) aboveis from 10 ppm to 10,000 ppm relative to the weight of the reactionsolution.
 10. The process of producing a water-soluble polymerdispersion as set forth in claim 1, wherein the viscosity-increasesuppressor is the member of the group which is a reaction productobtained by reacting (meth)acrylic cationic polymer with a compound thatgenerates radicals in an oxidizing atmosphere.
 11. The process ofproducing a water-soluble polymer dispersion as set forth in claim 1,wherein the viscosity-increase suppressor is the member of the groupwhich is a reactoin product obtained by reacting (meth)acrylic cationicpolymer with an oxidant.